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5G NR-Master Information Block (NR-MIB)

Over all structure of MIB and SIB in NR is almost similar to LTE and other legacy technologies. However there is a major difference related to the periodical transmission of SIBs. In LTE and other legacy technologies the SIBs are broadcasted priodically regardless of whether UE wants it or not. But, in New Radio (NR) there are two versions of SIBs. One is being transmitted periodically like LTE and other is being transmitted only on-Demand i.e. when requested by UE.

It included the necessary parameters required to decode SystemInformationBlockType1 (SIB1)

Its priodicity is about 80 ms and with in this 80 ms repetitive transmission happens

It is transmitted on OFDM symbol 1,2,3 .

It uses 0 to 239 sub carrier number on symbol 1 & 3, where as on symbol 2 it uses subcarried number 0 to 47 and 192 to 239 as per TS 38.211.

MIB/SIB signalling call flow:

Signalling radio bearer: N/A

RLC-SAP: TM

Logical channel: BCCH

Direction: Network to UE

RRC Parameters for Master Information Block:

MIB ::= SEQUENCE {

systemFrameNumber BIT STRING (SIZE (6)),

subCarrierSpacingCommon ENUMERATED {scs15or60, scs30or120},

ssb-SubcarrierOffset INTEGER (0…15),

dmrs-TypeA-Position ENUMERATED {pos2, pos3},

pdcch-ConfigSIB1 INTEGER (0…255),

cellBarred ENUMERATED {barred, notBarred},

intraFreqReselection ENUMERATED {allowed, notAllowed},

spare BIT STRING (SIZE (1))

}

Parameters Description:

systemFrameNumber : Similar to LTE, NR does have a 10 bit System Frame Number start from 0 to 1023. MIB carries 6 most significant bit (MSB) of the 10 bits and remaining 4 LSB of the SFN are conveyed in the PBCH transport block as part of channel coding (i.e. outside the MIB encoding).

subCarrierSpacingCommon: Indicates the Subcarrier spacing for SIB1, Message 2/4 for initial access and System Information-messages. It can have a values 15 and 30 kHz valid for carrier frequencies < 6GHz; Values 60 and 120 kHz are applicable for carrier frequencies > 6GHz

ssb-subcarrierOffsetindicates the frequency domain offset between SSB and the overall resource block grid in number of subcarriers. This field may indicate that this cell does not provide SIB1 and that there is hence no common CORESET. In this case, the field pdcch-ConfigSIB1 may indicate the frequency positions where the UE may (not) find a SS/PBCH with a control resource set and search space for SIB1

dmrs-TypeA-Position: Indicates Position of (first) DL DM-RS. It corresponds to L1 parameter ‘DL-DMRS-typeA-pos’

pdcchConfigSIB1: It is corresponds to RMSI-PDCCH-Config in TS 38.213 [13], section 4.1. Determines a bandwidth for PDCCH/SIB, a common ControlResourceSet (CORESET) a common search space and necessary PDCCH parameters. If the field ssb-SubcarrierOffset indicates that SIB1 is not present, the field pdcch-ConfigSIB1 indicate the frequency positions where the UE may find SS/PBCH block with SIB1 or the frequency range where the network does not provide SS/PBCH block with SIB1 (see TS 38.213 [13], section 13).

cellBarred indicates whether the cell allows UEs to camp on this cell as per specification TS 38.304

intraFreqReselection indicates if Intra frequency cell reselection is Allowed or notAllowed. It controls cell reselection to intra-frequency cells when the highest ranked cell is barred, or treated as barred by the UE as specified in TS 38.304